newbie ``print`` question

[gwhite]

On Sep 2, 3:43 pm, MRAB <pyt... at mrabarnett.plus.com> wrote:
> On 02/09/2012 21:58, gwhite wrote:
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> > On Sep 2, 1:16 pm, Dave Angel <d... at davea.name> wrote:
> >> On 09/02/2012 03:50 PM, gwhite wrote:
>
> >> > On Sep 2, 12:43 pm, Dave Angel <d... at davea.name> wrote:
> >> >> On 09/02/2012 03:34 PM, gwhite wrote:
>
> >> >>> <snip>
> >> >>> btw, I also thought the default "add a CR LF" to the end was odd too.
> >> >>> But at least that one had a simple way out.
> >> >> But it (print on Python 2.x) doesn't, unless you're stuck on Windows.
> >> >> And even then, you can prevent it by using a 'b' in the mode.
> >> > Yes, I'm using windows.  What is "'b' in the mode?"  The help for
> >> > print says:
>
> >> > A ``'\n'`` character is written at the end, unless the ``print``
> >> > statement ends with a comma.  This is the only action if the statement
> >> > contains just the keyword ``print``.
>
> >> > So I followed with a comma to stop the default CR LF insertion.
>
> >> You're correct;  the best way to suppress the newline at the end of
> >> print is to use the trailing comma.  But since print is for lines, it
> >> usually is a good default.  If you don't want to get any extra
> >> characters, just use write().  It takes a string, and outputs exactly
> >> what it's given.
>
> >> I assumed you were complaining about the conversion of newline to
> >> carriage-return-newline, which is done by default on Windows, and can be
> >> suppressed by opening the file with "b" as the mode parameter.
>
> > Sorry, I was a little vague on the newline stuff.
>
> > In any case, I've learned I should probably avoid the comma, if
> > looking at 3.x:
>
> >>>> from __future__ import print_function
> >>>> print('a=%.1f,' % 1.0),;print('b=%.1f' % 2.0)
> > a=1.0,
> > (None,)
> > b=2.0
>
> Explanation:
>
> With 'print' as a function, the first 'print' prints the result of
> "'a=%.1f,' % 1.0" and then returns None. The trailing comma makes that
> into a tuple (None,), which is printed by the interactive interpreter
> as such.
>
> In other words:
>
>  >>> None,
> (None,)
>  >>>
>
> The second prints the result of "'b=%.1f' % 2.0" and then returns None.
> The interactive interpreter, recognising that it's only None, doesn't
> bother to print it.
>
> In other words:
>
>  >>> None

Thanks, that makes sense.

It does look like 2.7 & 3.3 don't parse the comma the same way.  Just
to repeat, since I didn't give the exact same line to both versions of
Python:

2.7
>>> print('a=%.1f,' % 1.0),;print('b=%.1f' % 2.0)
a=1.0, b=2.0

This has been more informative than I thought it was going to be.